The present invention relates to a multicolor image-forming material and a multicolor image formation method for forming a high resolution full color image by use of a laser beam. In particular, the invention relates to a multicolor image-forming material and a multicolor image formation method useful for preparing a color proof (DDCP: direct digital color proof) or a mask image in the printing field from a digital signal by laser recording.
In the graphic art field, printing of a printing plate is carried out using a set of color separation films prepared from a color original by use of a lith film. In general, a color proof is prepared from the color separation films for checking errors in a color separation process and necessity of color correction before final printing (actual printing operation). The color proof has been desired to realize high resolving power which enables high reproducibility of a medium image, and to have performances such as high process stability. Further, for obtaining the color proof approximating to actual printed matter, materials used for the actual printed matter such as final print paper (an actual printing paper) as a substrate and a pigment as a colorant are preferably used as materials used for the color proof. As a method for preparing the color proof, a dry method using no developing solution is highly desired.
As the dry method for preparing the color proof, a recording system of directly preparing the color proof from a digital signal has been developed with the recent spread of the electronic system in the preliminary process of printing (prepress field). Such an electronic system is employed for preparing the color proof of particularly high quality, and generally reproduces a halftone dot image of 150 lines/inch. For recording the proof of high image quality from the digital signal, a laser beam which can be modulated by the digital signal and make recording light thin is used as a recording head. Accordingly, it becomes necessary to develop an image-forming material exhibiting high recording sensitivity to the laser beam and showing high resolving power which makes it possible to reproduce highly fine halftone dots.
As an image-forming material used in a transfer image formation method using a laser beam, there is known a heat melt transfer sheet comprising a support having provided thereon a light-heat conversion layer absorbing a laser beam to generate heat and an image formation layer in which a pigment is dispersed in a component such as heat-meltable wax or binder, in this order (Japanese Patent Laid-Open No. 58045/1993). In the image formation method using this image-forming material, heat generated in a laser beam-irradiated region of the light-heat conversion layer melts the image formation layer corresponding to the region to transfer an image onto an image receiving sheet arranged by lamination on the transfer sheet, thereby forming a transferred image on the image receiving sheet.
Further, Japanese Patent Laid-Open No. 219052/1994 discloses a heat transfer sheet comprising a support having provided thereon a light-heat conversion layer containing a light-heat conversion material, a heat release layer having an extremely thin thickness (0.03 xcexcm to 0.3 xcexcm) and an image formation layer containing a colorant, in this order. In this heat transfer sheet, irradiation of a laser beam reduces the bonding force between the image formation layer and the light-heat conversion layer bonded by intervention of the heat release layer to form a highly fine image on an image receiving sheet arranged by lamination on the transfer sheet. In the image formation method using the heat transfer sheet, so-called xe2x80x9cablationxe2x80x9d is utilized. Specifically, the heat release layer is partly decomposed to vaporize in a region irradiated with the laser beam, which causes the bonding force between the image formation layer and the light-heat conversion layer in that region to be weakened to transfer the image formation layer of that region onto the image receiving sheet laminated thereon.
These image formation methods have the advantages that final print paper provided with an image receiving layer (adhesive layer) as an image receiving sheet material can be used, and that a multicolor image can be easily obtained by transferring images different in color one after another onto an image receiving sheet. In particular, the image formation method utilizing ablation has the advantage that a highly fine image can be easily obtained, and is useful for preparing a color proof (DDCP: direct digital color proof) or a highly fine mask image.
In the progress of DTP circumstances, an intermediate film taking-out process is removed in the use of CTP (computer to plate), and the need for a proof according to the DDCP system has become strong, rather than the need for proof printing or a proof of the analog system. In recent years, large-sized DDCP having higher quality and stability and excellent in print agreement has been desired.
According to laser heat transfer systems, printing at high resolution is possible, and the systems include (1) a laser sublimation system, (2) a laser ablation system and (3) a laser melt system.
However, all of the above-mentioned respective systems have the problem that the recording halftone dot form is not sharp. The laser sublimation system of (1) has the problems that the approximation to printed matter is insufficient, because a dye is used as a colorant, and that the contour of a halftone dot is blurred, resulting in insufficient resolution, because the colorant is sublimated. On the other hand, the laser ablation system of (2) is good in the approximation to printed matter, because a pigment is used as a colorant, but has the problem that the contour of a halftone dot is blurred, resulting in insufficient resolution, similarly to the sublimation system, because the colorant is scattered. Further, the laser melt system of (3) also has the problem that no clear contour is obtained, because a melt flows.
Furthermore, when the difference in size between the heat transfer sheet and the image receiving sheet is small, a proper vacuum adhesion state can not be maintained in fixing the respective sheets to a recording drum by vacuum suction, so that the degree of vacuum is decreased to deteriorate the transferring properties of the image formation layer. On the other hand, when the difference in size is large, air accumulation is developed between the transfer sheet and the recording drum, resulting in a failure to obtain a good vacuum adhesion state.
In addition, when the difference in size between final paper and the image receiving sheet is small, wrinkles caused by slippage between the samples are liable to be developed. Conversely, when the difference in size is large, there is much waste, resulting in disadvantageous cost.
In the multicolor image-forming material according to the invention, the high process stability has been desired as described above. For example, the image receiving sheet is required to have good conveying properties, and further to have good accumulation properties, because a plurality of recorded cut image receiving sheets need to be accumulated.
In the heat transfer sheet on which a color image is formed, a defect of the image significantly reduces the commercial value. One of the causes of the image defect is that a part of the image formation layer is broken by a scratch, resulting in a failure to transfer that portion of the image, which can cause the defect of the image itself. The reason for this is that a surface of the heat transfer sheet is rubbed with a back face in producing, processing and printing the heat transfer sheet to scratch it. In particular, when the area of the image is large, the probability of occurrence of the image defect increases with the size of the image. Accordingly, in the case of the heat transfer sheet having a large image area, it is required that the image defect is more difficult to develop.
For preventing such an image defect, Japanese Patent Laid-Open No. 270154/1993 describes a method of using a specific polyester-acrylic styrene copolymer as a binder for an image formation layer. Further, there is also used a method of providing a protective layer on an image formation layer, thereby preventing an image defect.
It is possible to decrease the frequency of occurrence of the image defect caused by the scratch to some degree. However, the number of the image defects in one image plane is proportional to the image area, so that when the image area is increased, a problem is practically encountered. Further, the employment of the method of providing the protective layer on the image formation layer for preventing the image defect has raised the problem that the sensitivity of a heat-transferred image is lowered.
It is therefore an object of the invention to provide a large-sized DDCP having high quality and stability and excellent in print agreement. Specifically, the object of the invention is to provide a multicolor image-forming material and a multicolor image formation method which achieve that (1) a heat transfer sheet is not affected by an illuminating light source, even compared with a pigment colorant and printed matter, and excellent in sharpness of a halftone dot and stability by transfer of a colorant film, (2) an image receiving sheet can stably, securely receive an image formation layer of a laser energy heat transfer sheet, (3) transfer to final paper is possible corresponding to paper of 64 g/m2 to 157 g/m2 such as art (coated) paper), mat paper and fine enamel paper, and delicate texture depiction and accurate reproduction of a paper white portion (high-key portion) are possible, and (4) extremely stable transfer releasability is obtained. Further, the object of the invention is to provide a multicolor image-forming material and a multicolor image formation method which can form an image good in image quality and stable in transfer density on an image receiving sheet, even when laser recording is conducted at high energy by multiple laser beams under different conditions of temperature and humidity. Still further, the object of the invention is to provide a multicolor image-forming material and a multicolor image formation method which can prevent poor vacuum adhesion and wrinkles developed depending on the difference in size between the heat transfer sheet and the image receiving sheet and the difference in size between final paper and the image receiving sheet.
Another object of the invention is to provide a multicolor image-forming material provided with an image receiving sheet excellent in conveying properties and accumulation properties, having high process stability, and easily providing a highly fine image such as a color proof or a highly fine mask, and a multicolor image formation method using the same.
A further object of the invention is to provide a multicolor image-forming material provided with a heat transfer sheet which can prevent an image defect caused by a scratch even when the area of an image is large, and can provide a heat-transferred image good in sensitivity.
According to the invention, there are provided:
(1) A multicolor image-forming material comprising:
an image-receiving sheet having an image-receiving layer and a support; and
at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which each of the thermal transfer sheets has a different color,
wherein a multicolor image is formed by: superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer; irradiating the image-forming layer in each of the at least four thermal transfer sheets with a laser beam; transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to form an image; and transferring the image on the image-receiving layer onto an actual printing paper, and
each of the at least four thermal transfer sheets has a recording area being defined by a product of a length of 515 mm or more and width of 728 mm or more, and each of the at least four thermal transfer sheets is larger in each of a length-wise and a width-wise direction than the image-receiving sheet by 20 mm to 80 mm, and the actual printing paper is larger in each of a length and a width than the image-receiving sheet by 5 mm to 100 mm.
(2) A multicolor image-forming material comprising:
an image-receiving sheet having an image-receiving layer and a support; and
at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which each of the thermal transfer sheets has a different color,
wherein a multicolor image is formed by: superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer; irradiating the image-forming layer in each of the at least four thermal transfer sheets with a laser beam; and transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to form an image, and
the dynamic frictional force between an image-receiving surface on the image-receiving sheet and a back surface on the opposite side thereof is 30 gf to 120 gf.
(3) The multicolor image-forming material according to the item (2), wherein the dynamic frictional force is 50 gf to 80 gf.
(4) The multicolor image-forming material according to the item (2), wherein each of the at least four thermal transfer sheets has a recording area being defined by a product of a length of 515 mm or more and width of 728 mm or more.
(5) The multicolor imaging-forming material according to any one of the items (1) to (4), wherein a surface of the image-forming layer in each of the at least four thermal transfer sheets has a scratch resistance of 30 g or more, when the surface is scratched at a rate of 1 cm/second with a needle having a curvature radius of 0.25 mm.
(6) The multicolor imaging-forming material according to the item (5), wherein the scratch resistance is 220 g or more.
(7) The multicolor image-forming material according to any one of the items (1) to (6), wherein the irradiated area of the image-forming layer is transferred onto the image-receiving layer in the image-receiving sheet in a thin film.
(8) The multicolor image-forming material according to any one of the items (1) to (7), wherein the at least four thermal transfer sheets contain yellow, magenta, cyan and black thermal transfer sheets.
(9) The multicolor image-forming material according to any one of the items (1) to (8), wherein each of the image-forming layers in the at least four thermal transfer sheets has a ratio of an optical density (OD) to a layer thickness: OD/layer thickness (xcexcm unit) of 1.50 or more, and the transferred image onto the image-receiving layer has a resolution of 2400 dpi or more.
(10) The multicolor image-forming material according to any one of the items (1) to (9), wherein the transferred image onto the image-receiving layer has a resolution of 2600 dpi or more.
(11) The multicolor image-forming material according to any one of the items (1) to (10), wherein each of the image-forming layers in the at least four thermal transfer sheets has a ratio of an optical density (OD) to a layer thickness: OD/layer thickness (xcexcm unit) of 1.80 or more.
(12) The multicolor image-forming material according to any one of the items (1) to (11), wherein the image-forming layer in each of the at least four thermal transfer sheets and the image-receiving layer in the image-receiving sheet each has a contact angle with water of from 7.0 to 120.0xc2x0.
(13) The multicolor image-forming material according to any one of the items (1) to (12), wherein each of the image-forming layers in the at least four thermal transfer sheets has a ratio of an optical density (OD) to a layer thickness: OD/layer thickness (xcexcm unit) of 1.80 or more, and the image-receiving layer in the image-receiving sheet has a contact angle with water of 86xc2x0 or less.
(14) The multicolor image-forming material according to any one of the items (1) to (13), wherein each of the image-forming layers in the at least four thermal transfer sheets has a ratio of an optical density (OD) to a layer thickness: OD/layer thickness (xcexcm unit) of 2.50 or more.
(15) The multicolor image-forming material according to any one of the items (1) to (14), wherein each of the at least four thermal transfer sheets has a recording area being defined by a product of a length of 594 mm or more and width of 841 mm or more.
(16) A method for forming a multicolor image, which comprises:
preparing: an image-receiving sheet having an image-receiving layer and a support; and at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which the at least four thermal transfer sheets have at least four colors including yellow, magenta, cyan and black, in which each of the at least four thermal transfer sheets has a different color, and each of the at least four thermal transfer sheets has a recording area being defined by a product of a length of 515 mm or more and width of 728 mm or more, and each of the at least four thermal transfer sheets is larger in each of a length-wise and a width-wise direction than the image-receiving sheet by 20 mm to 80 mm;
superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer;
irradiating the image-forming layer in each of the at least four thermal transfer sheets from the side of the support with a laser beam; and
transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to form a image; and
transferring the image on the image-receiving layer onto an actual printing paper, wherein the actual printing paper is larger in each of a length-wise and a width-wise direction than the image-receiving sheet by 5 mm to 100 mm.
(17) A method for forming a multicolor image, which comprises:
preparing: an image-receiving sheet having an image-receiving layer and a support; and at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which the at least four thermal transfer sheets have at least four colors including yellow, magenta, cyan and black, and each of the at least four thermal transfer sheets has a different color, and the dynamic frictional force between an image-receiving surface on the image receiving sheet and a back surface on the opposite side thereof is 30 gf to 120 gf;
superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer;
irradiating the image-forming layer in each of the at least four thermal transfer sheets from the side of the support with a laser beam; and
transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to form a image.